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Review of current information on campylobacter in poultry other than chicken and how this may contribute to human cases
Project Code: B15019
Lyne, A ;
Health Protection Agency
University of Bristol
Little, C; Gillespie, I; Owen, R;
ADAS Poultry Team
Campylobacters are the most frequent cause of acute bacterial diarrhoea in the United Kingdom and other industrialised countries. Campylobacteriosis is usually a self-limiting but debilitating and painful disease that has enormous an economic impact in terms of treatment costs, lost production, and human welfare.
There is no doubt that poultry is a major source of campylobacters and there is scope for cross-contamination of other foods if contaminated poultry is introduced into the kitchen. This report examines the role that poultry other than chicken may play in Campylobacter infections in humans.
The UK turkey sector has polarised into large all year round production (AYR) and generally, small-scale seasonal production. Around 17 million turkeys are slaughtered in the UK each year – around 10 million of these are produced for the Christmas market. Just over 1.1 million turkeys are produced by small-scale seasonal turkey producers. There are two major producers of AYR turkeys and around 600 producers of seasonal turkeys - seasonal production is often a very important source of income to general farmers. UK turkey poult placings have dropped by 58% in the last 10 years as UK producers struggle to compete with cheap imports of turkey meat. The UK turkey industry contributes £365 million (measured at retail level) to the UK economy. This equates to 10.7% of the total contribution that the UK poultry sector makes to the UK economy.
Producers of turkey meat have tried hard to convince consumers to eat turkey all year round and to some extent have succeeded. However retail sales figures indicate that the total sales of turkey meat are, at best, static, although value has increased.
The UK duck industry is dominated by 4 major companies who produce, process and market ducks. Around 19 – 20 million ducks are produced in the UK each year. The largest production / processing company produces about half of this total, with three other companies producing and processing the remaining 9 – 10 million birds. Duck production is not seasonal.
The UK goose sector is almost exclusively comprised of seasonal production. One large company dominates the goose sector. Around 300,000 geese are produced each year in the UK. Approximately 300 producers rear geese for the Christmas market.
Duck and goose meat have gained slightly in popularity from consumer desire to ring the changes and opt for something different with the option to buy more prepared cuts. However, these remain essentially niche sectors. Sales of wild game have increased slightly but this has been met almost exclusively by imports.
There is only limited testing carried out for Campylobacter by producers and processors, sometimes because a particular customer has requested some monitoring or for general information. The information is gathered but not necessarily used as at present there is no practical advice to the industry on practical measures that can be taken to reduce Campylobacter incidence.
There is some concern amongst researchers about the testing regimes for Campylobacter carried out by some commercial laboratories, even those who are accredited. Also the absence of any quantification data makes it difficult to draw firm conclusions on the significance of the results that are available. This is supported by the comments from two producers who indicated that a change in laboratory had markedly affected the number of positive findings of Campylobacter.
There is evidence that some turkey producers find Campylobacter quite frequently (up to 50% incidence) whereas others do not but there is insufficient testing to draw scientific conclusions. In the duck sector there are clearly differences of opinion about likely or actual incidence of Campylobacter – the reasons for this difference is unclear.
Colonisation of turkey, duck, goose and game reared for meat, such as pheasants and wood pigeons, with campylobacters has been documented both in the UK and elsewhere. There is also evidence that when turkey, guinea fowl and squab are slaughtered the same types of campylobacters found on carcasses can also be found in the intestinal contents of the birds.
If the two recent UK retail surveys are combined the prevalence of Campylobacter in turkey and game bird meat was significantly lower than in chickens and the average prevalence were 34, 42 and 61%, respectively. However, it should be noted that much fewer samples of retail turkey (214) and game bird meat (112) than chickens (1778) were sampled and thus may introduce a bias in the comparison made. It is likely that as for chicken the prevalence will vary dependent on what samples are taken, location and time of year. The lower prevalence found in turkey and game bird meat in the combined UK surveys could suggest lower numbers of campylobacters on turkey and game bird meat but there are no UK data available and only two reports have documented numbers of campylobacters in non-chicken poultry samples.
There is evidence, albeit based on a relatively small number of studies, that C. jejuni and C. coli are the species that most commonly colonise turkeys, ducks and geese. The studies reviewed included results on birds at the farm level as well as on samples taken at retail outlets. The relative proportions of the two species vary between studies depending on geographic location and the nature of the surveys done. C. coli was significantly more prevalent in game bird (but not turkey) meats than in chicken meat samples in two UK retail surveys but much fewer isolates from turkey (53) and game bird (33) than chicken (895) meats were examined.
Isolates of Campylobacter from several studies have been typed by variety of methods, both phenotypic and genotypic. Results obtained indicate the diversity of such isolates. Results from HS serotyping and MLST indicate that several of the types found in turkeys, ducks and geese are shared with those causing human disease.
The extent of the overlap is difficult to quantify meaningfully because of the small numbers of isolates tested to date and the diversity of the samples. Some interesting pointers are noted from overlap in the predominant MLST clonal types ST types: e.g. C. jejuni CC-45 and CC-21, which are relatively frequently associated with human disease can be found in ducks and geese, and it has been suggested that these maybe well-adapted to colonise a variety of hosts and survive between hosts. Likewise there is an overlap in the more common HS serotypes.
The review highlights many gaps in our knowledge in this area. Notably it would be interesting to have MLST data on the isolates from the LACORS/HPA survey to complement the phenotyping results and to provide a more comprehensive picture of the isolates from the UK retail red meats surveys.
As chicken is such a strong risk factor for human Campylobacter infection it is difficult to estimate the role of poultry other than chicken, although it is likely to be comparatively small. Nevertheless, microbiological and epidemiological evidence from this study suggests that a role clearly exists. There is a clear peak in Campylobacter infection around Christmas which is when most turkey is consumed. However examination of existing data does not provide the evidence of a link between consumption of turkey and this increased incidence.
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